Multiple input multiple output (MIMO) systems are wireless communications systems that may transmit signals utilizing a plurality of transmitting antennas, and/or receive signals utilizing a plurality of receiving antennas. Communications between MIMO systems may be based on specifications from the Institute of Electrical and Electronics Engineers (IEEE). A MIMO system that receives a signal Y may compute a channel estimate matrix, H, based on the received signal. The signal may comprise information generated from a plurality of information sources. Each such information source may be referred to as a spatial stream.
A MIMO transmitter may combine spatial streams to generate one or more RF chains. Alternatively, each RF chain may correspond to a distinct spatial stream. A group of RF chains may be concurrently transmitted from the transmitting MIMO system via a plurality of transmitting antennas. The signals concurrently transmitted by the plurality of transmitting antennas, referred to as spatial stream signals, may be represented as a transmitted signal vector X. The spatial stream signals xi (where i is a spatial stream index variable), which comprise the signal vector X, may propagate across a communication medium en route from the transmitting MIMO system to receiving MIMO system. The signal transfer characteristics of the communication medium may be represented by a channel matrix, H. A receiving MIMO system may utilize a plurality of receiving antennas when receiving the signals. The signals concurrently received by the plurality of receiving antennas may be represented as a received signal vector, R.
The MIMO communication system may be represented mathematically as follows:R=HX+N  [1]where R represents a column vector of signals received by each of a plurality of Nrx receiving antennas: r1, r2, . . . , and rNrx; X represents a column vector of signals transmitted by each of a plurality of Ntx transmitting antennas: x1, x2, . . . , and xNtx; H represents a matrix of channel estimates comprising Nrx rows and Ntx columns; and N represents a column vector of noise received by each of the Nrx receiving antennas: n1, n2, . . . , and nNrx. Statistically, the noise elements, ni, are typically considered to be independent and identically distributed complex Gaussian random variables.
In equation [1] each of the spatial stream signal values xi may be represented by one or more bits b1, b2, . . . , and bMOD(i). Each spatial stream signal value, which comprises the bits b1, b2, . . . , and bMOD(i), may be referred to as a “symbol”. The number of bits MOD(i) in each symbol may be determined based on the modulation type utilized for generating the corresponding spatial stream signal xi at the MIMO transmitter. Each value for the transmitted signal vector, X, may be represented as comprising the collective bits from the set of concurrently transmitted symbols. The total number of bits represented in vector X is a summation of values MOD(i) for the spatial streams identified by i=1, 2, . . . , and Nss.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.